Moisture present on particulate solids, such as coal, mineral ores, and other finely divided solids, causes serious problems when such solids are shipped or stored under low temperature or freezing conditions. When the moisture freezes, the ice thus formed acts as a powerful adhesive, binding the particles to each other and often to the sides of their container, if any, such as rail road car walls. For example, a rail road car of coal can be bound into a solid mass by the frozen moisture, which mass may even be adhered to the car itself, causing obvious serious problems in unloading. As further example, such particulate solids, if stored outside in piles during cold weather, may be frozen together by the freezing of the moisture, requiring breaking up before use, or transport to the site of use.
Both physical and chemical methods have been used to alleviate the problem, either by preventing or reducing such moisture freezing or as means to reduce the size of the frozen masses. Vibration and dynamiting have been used. Heating by means of fires, steam, and infra red heating have been used. These methods generally present safety problems and are uneconomic. Further, they are often ineffective or totally impractical when the freezing is severe.
As for chemical methods, sodium and calcium salts have been added to moisture-containing coal with some degree of success toward reducing the freezing problem. Such salts, however, contribute to the corrosion of all equipment contacted by the treated solids, and when used with coking coal are detrimental to the coking process. Thus this form of chemical treatment is lacking.
In U.S. Pat. No. 3,794,472 it has been disclosed that coal particle freezing problems are prevented by coating either the coal particles and/or the surfaces of their storage container with a composition comprising a hydrocarbon liquid which has emulsified therewith an aqueous solution of a polyhydric alcohol. In U.S. Pat. No. 3,298,804 the surface treatment of coal particles to prevent freezing problems with a composition of a liquid hydrocarbon and a surface-active composition in the class of substituted imidazolines is disclosed.
Ethylene glycol, generally admixed with water, also has been used for coating coal particles to reduce freezing problems. In comparison to salt treatment, ethylene glycol treatment is more expensive, but eliminates contribution to corrosion, presents no safety problems, and has no deleterious effects on the use of the coal so treated. Ethylene glycol based compostions, moreover generally are less expensive than hydrocarbon based compositions, but when applied at maximum levels considered commensurate with economic practicalities, its performance is disappointing.
There is a need for freeze conditioning compositions for treating finely divided particulate solids, such as coal, ores, and other such solids that contain moisture, to overcome the freeze problems in transportation and storage, that are more effective then ethylene glycol while at least in the same cost range as ethylene glycol.